"""
TINY interpreter scaffold built using:
- parser defined in tiny_parser.py
- executable statement AST classes defined in tiny_ast.py
- execution engine defined in tiny_engine.py

This module currently provides:
- main(): CLI entry point that reads a .tiny source file, parses it using the
  TINY grammar, and prepares for conversion to TinyNode-based AST.

Usage:
    python -m examples.tiny.tiny_run path/to/program.tiny [--dump]
"""
from __future__ import annotations

import argparse
import sys

import pyparsing as pp

from .tiny_parser import parse_tiny
from .tiny_ast import TinyNode
from .tiny_engine import TinyEngine


def explain_parse_error(src: str, err: pp.ParseBaseException) -> str:
    """Return a helpful, context-rich parse error string."""
    source_lines = src.splitlines()
    error_lineno = err.lineno
    lineno_len = len(str(error_lineno + 1))

    # Guard against last-line errors
    if err.lineno - 1 >= len(source_lines):
        source_lines.append("")

    *prelude, error_line, postlude = source_lines[max(error_lineno - 3, 0): error_lineno + 1]
    fragment = "\n".join(
        [
            *(f"{prelineno:>{lineno_len}}:  {line}" for prelineno, line in
              enumerate(prelude, start=error_lineno - len(prelude))),
            f"{error_lineno:>{lineno_len}}: >{error_line}",
            f"{error_lineno + 1:>{lineno_len}}:  {postlude}",
        ]
    )

    return fragment + "\n\n" + err.explain(depth=0)


def main(argv: list[str] | None = None) -> int:
    parser = argparse.ArgumentParser(description="Run a TINY program using the TINY interpreter scaffold.")
    parser.add_argument("source", help="Path to the .tiny source file")
    parser.add_argument("--dump", action="store_true", help="Dump parsed structure (debug)")
    args = parser.parse_args(argv)

    try:
        with open(args.source, "r", encoding="utf-8") as f:
            source_text = f.read()
    except OSError as exc:
        print(f"Error reading {args.source}: {exc}", file=sys.stderr)
        return 2

    try:
        parsed = parse_tiny(source_text)
    except pp.ParseBaseException as exc:
        # Print helpful location info
        print(explain_parse_error(source_text, exc))
        return 3

    if args.dump:
        # Pretty-print the primary structure for inspection
        print(parsed.dump())
        exit()

    # Instantiate the engine that will hold globals, functions, and frames
    engine = TinyEngine()

    # initialize engine with parsed globals
    initialize_engine(engine, parsed.program)

    # Execute scripts "main" function
    main_node = engine.get_function("main")
    main_node.execute(engine)
    return 0


def initialize_engine(engine: TinyEngine, program: pp.ParseResults) -> None:
    # Register all top-level function definitions: build function nodes and signatures
    if "functions" in program:
        for fdef in program.functions:
            # Build a function node with a prebuilt body
            fn_node_class = TinyNode.from_statement_type(fdef.type)
            fn_node = fn_node_class.from_parsed(fdef)

            # Register function node for runtime use
            engine.register_function(fn_node.name, fn_node)

    # Register any top-level globals if they exist (grammar may not provide these)
    if "globals" in program:
        for g in program.globals:
            try:
                dtype = str(g.datatype)
                # Handle one or more variable declarations in a decl stmt
                decls = g.decls if hasattr(g, "decls") else []
                for d in decls:
                    name = d.name
                    init_val = d.get("init") if isinstance(d, pp.ParseResults) else None
                    engine.declare_global_var(name, dtype, init_val)
            except Exception:
                # Best-effort: skip malformed/unsupported global forms
                continue

    # Build AST node for main() and register it as a function
    main_group = program.main
    main_node_class = TinyNode.from_statement_type(main_group["type"])
    main_node = main_node_class.from_parsed(main_group)
    engine.register_function("main", main_node)


if __name__ == "__main__":
    raise SystemExit(main())
